It's a common misconception that an 'inverter' system is one that heats as well as cools. But most systems offer both functions - so what's the difference between an inverter and non-inverter?

A non-inverter is a basic model which operates at a fixed speed, simply controlling temperature by switching on/off alternately. Commonly sold in DIY superstores, these are significantly cheaper to buy but consume up to 40% more electricity, because of this fluctuation. Alternatively, a more sophisticated 'inverter' has a variable-speed compressor which constantly regulates to the desired temperature – a more economic method of operation and A-graded for energy-efficiency. Although costing more to buy, inverters offer a wise long-term investment.

Most brands offer both formats for a standard 1-room system. So, to decide which is best for you, consider how frequently (and at what level) the system will be used. For example, holiday clients often run air-con at maximum settings for long periods – but they don't pay the bills!